ABSTRACT

Consistent asymmetries between the left and right sides of animal bodies are common. For example, the internal organs of vertebrates are left-right (L-R) asymmetric in a stereotyped fashion. Other structures, such as the skeleton and muscles, are largely symmetric. This Review considers how symmetries and asymmetries form alongside each other within the embryo, and how they are then maintained during growth. I describe how asymmetric signals are generated in the embryo. Using the limbs and somites as major examples, I then address mechanisms for protecting symmetrically forming tissues from asymmetrically acting signals. These examples reveal that symmetry should not be considered as an inherent background state, but instead must be actively maintained throughout multiple phases of embryonic patterning and organismal growth.

Footnotes

Competing interests

The authors declare no competing or financial interests.

Funding

D.T.G. is funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases K99/R00 award mechanism, by the Donald E. and Delia B. Baxter Foundation and by the University of Oregon. Deposited in PMC for release after 12 months.

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